Since injection is of such great importance, great efforts are being made in developing this process, the materials used and the sequence of operations. If done correctly, complete filling of the encasing tube with mixture can be ensured. There nevertheless remains a certain amount of uncertainty about whether errors may have occurred during mixing and injection of the mixture. Extensive measures are often taken to eliminate this uncertainty and exclude faulty manipulations. For example, a hole is drilled in the region of the anchorage, and the filling is assessed visually. An alternative is the use of transparent covers which permit visual checking of the tendon filling during and after the setting process at accessible locations. In addition, in individual cases, the filling of the tendon is checked at points using radar.
Most of these measurements cannot be carried out until after successful injection, however, and require considerable time, effort and investment in measuring. Some locations are not accessible for these methods. During the injection procedure, however, the time up to completion of the operation is severely limited by the incipient setting of the mixture.
It is therefore important to have information during the injection operation about a possibly insufficient filling with mixture at all critical 20 locations. Only in this way can a higher degree of filling be achieved through additional measures.
It has been proposed that this control is possible by means of a filling sensor that detects the wetting of the sensor by mixture, as described in JP2000230915.
Filling the tendon with mixture does not suffice in every case to ensure corrosion protection, however. Thus corrosion damage can occur even though the tendon has been completely filled with mixture. This is possible, for example, if a blast furnace cement with minimal alkalinity or mixing water polluted with chloride is used. Under certain circumstances, such situations cannot be excluded even with optimal quality control. Chlorides can also penetrate subsequently into the encasing tube through leaky places in the concrete, and, at high enough concentrations, can trigger corrosion.